Zimmerman has said he shot and killed Martin on Feb. 26 in Sanford, Fla., in an act of self-defense. The incident became a national story as Martin's family and supporters have questioned why police took so long to arrest and charge Zimmerman and whether the black teen was the victim of racial profiling before and after his death.

Zimmerman has been charged with second-degree murder. An image like this could play a central role in his defense because Zimmerman says Martin was banging his head against concrete, so he shot him to protect his life.

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